s3: enforce authentication and JSON error format for Iceberg REST Catalog (#8192)

* s3: enforce authentication and JSON error format for Iceberg REST Catalog

* s3/iceberg: align error exception types with OpenAPI spec examples

* s3api: refactor AuthenticateRequest to return identity object

* s3/iceberg: propagate full identity object to request context

* s3/iceberg: differentiate NotAuthorizedException and ForbiddenException

* s3/iceberg: reject requests if authenticator is nil to prevent auth bypass

* s3/iceberg: refactor Auth middleware to build context incrementally and use switch for error mapping

* s3api: update misleading comment for authRequestWithAuthType

* s3api: return ErrAccessDenied if IAM is not configured to prevent auth bypass

* s3/iceberg: optimize context update in Auth middleware

* s3api: export CanDo for external authorization use

* s3/iceberg: enforce identity-based authorization in all API handlers

* s3api: fix compilation errors by updating internal CanDo references

* s3/iceberg: robust identity validation and consistent action usage in handlers

* s3api: complete CanDo rename across tests and policy engine integration

* s3api: fix integration tests by allowing admin access when auth is disabled and explicit gRPC ports

* duckdb

* create test bucket

weed/s3api/auth_security_test.go

@@ -98,8 +98,8 @@ func TestReproIssue7912(t *testing.T) {
 		var nilIdentity *Identity
 		// Test isAdmin guard
 		assert.False(t, nilIdentity.isAdmin())
-		// Test canDo guard
-		assert.False(t, nilIdentity.canDo(s3_constants.ACTION_LIST, "bucket", "object"))
+		// Test CanDo guard
+		assert.False(t, nilIdentity.CanDo(s3_constants.ACTION_LIST, "bucket", "object"))
 	})
 
 	t.Run("AuthSignatureOnly path", func(t *testing.T) {